How do you debug a visual studio add-in that throws an exception during loading?

Question

I'm working on an add-in for Visual Studio 2005 in C#, and while everything works if I launch it from the debugger, actually installing it (adding the .addin and .dll to the add-ins directory) results in it not working. When Visual Studio loads it, I get the error "The Add-in "MyAddin" failed to load or caused an exception." With Error Message: Unspecified error, with error number: 80004005, and then offers me the ability to disable it.

From here, I can't figure out how to debug that load process in order to figure out what's going on. I can't seem to attach to the dll before it's loaded, or specifically launch the dll in a fashion that causes it to load in the same fashion. I also can't attach when the error message is up.

How on earth do I do this?

Edit: I'm starting to believe this isn't a problem with my code so much as the .addin file. Given that I can't break the code in the constructor, and the MyAddin - For Testing.addin works, perhaps it is a larger issue with the generated MyAddin.addin file.

Answer 1

Add the line below at the beginning of your code. This will prompt you if you'd like to open up a VS window to debug (see MSDN). Then you can step through your code as needed.

Debugger.Break();

There is a benefit of using this method over "Attach to Process" in that you won't have to worry about attaching to the process each time and before the exception occurs.

Answer 2

The easiest way, which might not trigger the same exception:

• Disable the load on startup.
• Start 2 Visual Studio instances.
• Use Tools -> Attach to Process to attach it as a debugger to the other instance.
• Optionally also set Debug -> Exceptions to break on all CLR exceptions.
• Load the addin in the debuggee

Answer 3

Maybe it requires a native side break point on appearances of 80004005 in devenv.exe. This usually requires you are familiar with WinDbg or so on.

If your company has a support contract with Microsoft, open a support case via http://support.microsoft.com to involve the experts.

Answer 4

After sleeping on it, I came back fresh and re-looked at everything. Turns out the generated .Addin file had a broken reference, and so was trying to load a non-existent file. After fixing the reference, everything works great (including 30 Break()s being called during visual studio start-up... but at least I know that was working.)